Almost-Island Universes
by September Watson
Summary: "You and I, John, were born billions and billions of years ago out of cold gases, dust, adrenaline, misplaced love, and a desire for an unnamed something that consumed us." In which Sherlock learns astronomy and writes John a letter before he leaves on the six-month mission. AU


**I went to a lecture last night involving astronomy, and I realized I had to write about it. I guess this is my birthday present to myself. Anyway, enjoy!**

* * *

My dearest John,

There is something I need to tell you, and I might as well tell you after I'm gone, because I'm scared. So scared.

Right now, I'm on a plane. You don't know this, but I won't be coming back to you. You're wearing a jumper with your gun in your back pocket and staring up at the sky and I know you'll walk away when Mary pulls you with her. If it were just you and I, you'd stay until the airplane was out of sight but even then wait until it grew dark to leave the airstrip. You'd linger for me, and you'd see this letter fall out of the window just a little ways away. John, you need to see this. I can't be gone fully unless you do.

Before I explain this, I need to tell you that I learned about astronomy for you. I searched online, I read books, I went to university lectures, I stared at the sky for hours and hours while you were living with Mary. As I looked and listened and understood, I realized that you and I, John, are galaxies.

We were born billions and billions of years ago, forming out of cold gases, dust, adrenaline, misplaced love, and belief in an unnamed something that consumed us. As everything swirled together, we discovered there were giant black holes at our centers, with gravity so strong that even light couldn't escape. I had hoped there were others like me, I just couldn't see far enough to identify you. I lived my whole life believing I was alone, believing all those groups of sparkling dust were just insignificant stars and planets with no connections to me.

I named the constellations after heroes and monsters, because I didn't know which one of them I would be.

Somewhere in my mind, I wondered if the other sparkling masses were universes as well, so far away that I just couldn't see where they were exactly. I didn't want to be an island. I didn't want to be by myself forever. I didn't know you were out there yet, but I knew somehow that you'd be a universe like me.

Late in my life, I looked up at the black emptiness around me and found that one of the clusters of stars (I called you a nebula without meaning to) had come closer to me. When I stared at it a little longer, I realized it was so much bigger than I thought. I do overlook details sometimes, but it's seldom enough that I refuse to remember.

As soon as I noticed that big nebula, I tried to figure out what it was, stared at you from every angle, calculated your distance, but I still didn't know anything. You were so complex, so intricate, so unpredictable. Beautiful. Like me. Your stars had different planets, and your eyes were softer, but you were always willing to run after me. I still thought of you like just another nebula for a while, even though you were a galaxy, when I should have known you would change me.

We interacted for a few short months, which was nothing and everything in a galaxy's time. My black hole grew smaller when I was around you, and bigger when your orbit carried you away from me, and many stars were born in your presence. I always wanted us to collide, no matter how much collateral damage would come from it.

Once I needed you, I built huge telescopes to find out if you were really a galaxy, and not another cluster of young stars that I could wean myself off of. I analyzed you, watched you, computed your data so many times it makes my head hurt thinking about it. And then, all of the sudden, I reached my magnification out as far as it could go, and found out how big and complicated and just everything you really were. A galaxy. A galaxy with a big black hole at its center that even light couldn't escape. An angel from the sky.

There are some discoveries that change entire universes. You were one of those, John Watson.

I don't know if you know this, but I fell in love with you. Just like that. I wanted you to never go, never leave, always stay with me. I'd never been in love before you, only had my gaze drawn by bright stars. But you, you were an entire galaxy within a person, swirling and changing and yet staying the same. I could have watched you forever.

One day, one of my constellations, Mycroft the Scorpion, poisoned me with the thought that a supermassive black hole wanted to suck me in, destroy me for years and only a moment. Moriarty. In reality, he was a quasar, bright, constantly burning up the matter being sucked into him. Perhaps, he told me, if I faded away, leaving only my memory in your eyes, Moriarty wouldn't be able to find me.

I didn't want to leave, my love. You must always remember that.

When I died, and I did indeed die, I became a shadow, a cosmic web of dust and cold gases again. Alone, flying through the black space with no purpose, no knowledge, no life, no love, no _light_. I'm sorry if my hands shake while I write this. My mind fractures when I think about the time without you.

I'm sorry. I'm so sorry, John. I'm sorry for everything, and I know you will never fully forgive me.

When I came back to you, I found something that made me so sad. You had a quasar of your own, a woman that drew you in and captured you, so that some part of your heart was her. Mary Morstan shone, didn't she? She shone like I did, but she was a sucking void of darkness and lies beneath. She fooled me too, and I wanted to warn you, but I physically could not break your heart, John. To do so would increase my own black hole's diameter by millions of light-years.

But I let it happen. I tried to let you go. Your orbit was spinning you far, far away from me, but if it made you happy, I couldn't have stood in your way. I killed Magnussen to let you live without his death hanging over your head because you are my weakness and always have been. I love you, and love isn't an advantage.

John, Mary's going to leave you. I can see it in the glances she throws your way, her 'habit' of not wearing her wedding ring, the makeup she wears when she 'goes out with friends'. She's going to leave as soon as the baby is born and thrust it upon you to raise by yourself. I wish you could see you're better off without Mary. I wish I could see your child, John. It's a girl.

I will die on this mission. I'll die without knowing what we could have been. I'll die remembering the look on your face as I fell. I'll die with you falling away from me. I'll die a galaxy, exploding into trillions and trillions of microscopic pieces and fire.

Let me go. Forget me, please, John. The collateral damage is too much to justify what I did.

All my belated love,

William Sherlock Scott Holmes-Watson

* * *

John watches the plane take off from a sitting position, staring at the sky after it's gone. Something doesn't feel right about the way Sherlock said goodbye to him, with the baby names, and Sherlock said he had something important to tell John, but he didn't say it. Why didn't he say it?

Mary leaves in the car; John will just get a taxi. It doesn't matter.

He is really exhausted. Even though she's his wife, Mary never notices things like that. Sherlock always knows, and John finds it comforting that he doesn't have to say anything. But not saying anything bites people in the arse, John thinks bitterly. Eventually, the truth will come out. He really wants coffee to keep him awake while he waits for the airstrip to go dark so he knows Sherlock's gone.

As John stares at the sky, he sees a fluttering object fall, but he can't seem to move from where he is. "Sherlock, you have to come back. I can't live like this much longer," he mumbles. "Something is going to detonate, and you won't be there to help me survive it."

...

When the sun is completely past the horizon, John stands up. Stars come out and twinkle a little as if in greeting. He's never seen the stars this close in a while, not since Afghanistan at least. There are some missing, John knows subconsciously. The light sources just flicker out every so often. They've lost the will to live, perhaps. Or the thing that made them live disappeared. As John looks at the sky, he remembers what it was to have lost a light.

He begins to walk down the airstrip, toward where the airplane was going, feet tracing the wheel paths on the ground. He walks and walks and walks and doesn't want to leave. This is the last place Sherlock was. It deserves to be recognized.

Kilometers pass, John thinks. He loses track of time as he goes. Seconds elongate so every arc second is 3600 times slower.

Ttttiiiicccckkkk ttttoooocccckkkk.

In this time, John finds an envelope with multiple pieces of clear tape securing it. It's laying on the ground, almost dejectedly, as if it's looking for a reader but hasn't found one. He picks it up, turns it over, and sees handwriting he knows all too well.

 _John_

Why would Sherlock not just give him this? Why did he have to throw it out the window of the plane? John fumbles with the very excessive amount of tape (which is quite out of character for the consulting detective) and finally manages to get the damn thing open.

 _My dearest John,_ it reads.

 _There is something I need to tell you, and I might as well tell you after I'm gone, because I'm scared. So scared._

* * *

6 months later

Sherlock, beat up and battered and probably in need of medical assistance, tiptoes up to his flat and opens the door. He winces at the creaking of the hinges that prove how long he's really been gone. Mrs. Hudson must have forgotten for months and months.

The stairs' creaking he's more used to, but he's quiet anyway. The door to 221B is closed. Sherlock searches around his coat for the key, remembering all the places on his body that he shouldn't be touching or moving, before finding it in his shirt pocket scratching against his picture of him and John the day they met. They looked happy, the detective thinks to himself. He almost wishes he could go back there, but it wasn't meant to be.

When he unlocks the door, he doesn't notice several key details that he normally would have had he not been injured and slept in the last two weeks. One, there is no dust. Two, the place is much cleaner than he had left it. And three, the most obvious, there is a baby monitor on the leg of the couch. But Sherlock just collapses on the nearest soft surface, in this case, John's old chair, and falls asleep.

...

John wakes up to the sound of his baby daughter gurgling in her crib. He smiles and takes her out, saying, "Good morning, love. Formula or formula for breakfast, hm?" She gives him her big, gray-eyed look, and John says, "Formula it is."

Elise Sherlock Watson was born April 6, on a stormy day. Mary only spent a few hours in labor, and when Elise was born, the skies cleared. John had always been a little bit superstitious, but when his daughter came into the world, he knew she was the only thing he ever needed. Sherlock was right about a lot of things. He should have seen her.

He was also right that Mary would leave John after she had Elise. John hoped Sherlock was wrong, but deep inside he knew something was off about her. After she left, John gave up on dating, quit his job, and lived at 221B taking care of his daughter. Mycroft refused to let John pay for anything, apparently having built a huge account in the bank with double the money John needed to live well.

John shrugs, settling Elise on his hip and walking down the hall to the kitchen. He should probably go to Tesco and buy milk, the two of them are almost out. Elise likes milk almost as much as Sherlock did, except she hasn't used it for experiments. "Here comes the sun, dododo, here comes the sun," John sings softly. "It's all right, dodododod-" He breaks off when he sees who's camped out in his chair.

"Sherlock?" The detective doesn't answer.

John walks around the chair a few times, his daughter clapping her hands. It looks like Sherlock, but John can do one thing to know for sure. He doesn't want to, but it's been the most successful way to get Sherlock out of his mind palace or to awaken. John hasn't seen his detective asleep in a very long time.

"Moriarty!"

The Sherlock-man jerks awake, hands in front of him to guard his face, and stands. "Where? John, get behind me!"

John stays where he is. Elise reaches her little hands out to Sherlock, but he doesn't notice. "John, you have to get behind me!"

"Sherlock, Moriarty's dead." John takes one of his detective's hands and laces his fingers through the other man's. "It's just you and me."

Sherlock looks up at him for the first time. The word he says carries everything he wanted to tell John over the six months he was gone, over the two years he died, over the years they'd known each other, over the ten billion years they'd been apart. "John?"

He smiles. "Yes, Sherlock. It's me."

The detective quickly comes forward and wraps his arms around his John and the baby. "I'm sorry. I'm so sorry, and I shouldn't be here. I need to leave you alone, but please, let me hold you just this once." He squeezes John so tight Elise protests in her almost-forming voice. "What's her name?"

"Elise Sherlock Watson."

Sherlock presses a kiss to her hair. "She's beautiful. She's so beautiful, John. And she looks like you."

"Not only does she look like me, she has other qualities of mine. And of yours, actually."

The detective frowns slightly. "My qualities? Elise is yours and Mary's child. She was never exposed to me."

John turns Sherlock's face so he can see him. "Yes, she was. She was around you as long as you were there. You know how I know that?"

"How?"

"She's smart, has your eyes, knows what a violin sounds like."

"I feel like there's something else."

John gently kisses Sherlock on the forehead. "She's a galaxy, just like you and I."

The detective freezes for a moment. "You read it?"

"I read it. And you know what?"

"Don't keep me in suspense please, John."

"We would have never been able to be island universes. We would have found a way together no matter how hard it was, no matter how much collateral damage, no matter how many billions of years it took. So stay here with me, raise Elise with me. I love you too."

Sherlock barely hesitates before saying, "Yes. Always."

* * *

The two galaxies collide, and form a larger galaxy with two black holes, but it shines brighter than any in existence. It is like they were always meant to be one.

* * *

 **So, happy birthday to me. I hope you guys enjoyed it! Read + review!**


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